A farmer rearing sheep, presented with complaints of fever and weakness for the last one month. There is generalised lymphadenopathy. There was also associated hepatomegaly Biopsy of liver showed non caseating granuloma. These are most likely due to infection with -

Ans. is D i.e., Brucella Melitensis The history of contact with animal (sheep) and the characteristic symptomatology & pathology ours the diagnosis of Brucella melitensis. All the organisms given in the question have animals as their natural host but they can also infect human. So the choice comes to Brucella melitensis because the patient has a history of contact with sheep. Brucella melitensis usually infects Goats, camel & sheeps Brucella canis usually infect Dogs Yersinia pestis infects Rodents(wild) Francicella tularemia Rabbits